Herrera told United's official website: "Signing for Manchester United is a dream come true. I have played at Old Trafford for Athletic Club in the UEFA Europa League and it was one of the highlights of my career so far.

"I have joined United to do all I can to help the team reach the club's objectives. Having arrived on Tuesday, I'm excited to now be living in Manchester and I can't wait for my first game in United's famous red shirt.

"I will never forget my time with Athletic Club and I'd like to thank the fans and staff for all their support and, above all, wish all my fantastic former teammates all the best for the future."

United assistant manager Ryan Giggs welcomed the signing and claimed Herrera is one of the best young players in Spain.

He said: "Ander is a fantastic young player, with great energy and creativity. We believe him to be one of the brightest young prospects in Spain and I am certain he will be a big hit with the United fans.

"I'm delighted he has made the decision to come to Manchester and play his part in the club's future. I'm looking forward to seeing him in action on our summer tour to America."

A statement read: "Athletic Bilbao thanks Ander Herrera for his dedication during the three seasons he has enjoyed the club and wishes him the best in his future sports projects."

He is also set to be the fourth most expensive player in the club's history, with his expected 28.8 million pound fee putting him behind only Juan Mata, Dimitar Berbatov and Rio Ferdinand.

United have made strengthening the centre of midfield a priority. Former manager Moyes failed in attempts to sign Cesc Fabregas, Thiago Alcantara, Daniele De Rossi, Sami Khedira and Herrera last summer.

And while Van Gaal opted not to pursue Fabregas and Toni Kroos, two targets Moyes had identified, the Netherlands manager has moved quickly to bring in Herrera.